1. Field of the Invention
The present invention pertains to an enclosure for electronics. In particular, the present invention pertains to a modular enclosure for housing electronic components. The modular container comprises interchangeable elements to expand or reduce the interior volume of the container.
2. Description of the Related Art
As seen in FIG. 1, conventional electronics enclosures 10 are typically constructed to include four sides 12, a top 14 and a bottom 16. In some instances, the bottom 16 is formed integrally with the sides 12. The top 14 and bottom 16, or top 14 only in the case of the latter, are then secured to the sides 12 in order to seal the enclosure and any circuit card assemblies therein.
Typical enclosures are sealed through a variety of methods. In one version, the top and bottom 12 and 14 are held in place around an intermediate section that forms or is integral with the sides 12 via a nut 20 and bolt 22 assembly. The bolt 22 passes through apertures or holes 24 in the corners of the top 12 and bottom 16, leaving the threaded end 26 accessible to thread a nut 20 thereon. The intermediate section may have matching passages 28 through which the bolt 22 passes in the walls and at positions corresponding to holes 24 in the top 14 and bottom 16. Alternatively, the top and bottom 14 and 16 have a skirt that extends beyond the outer perimeter of the intermediate section and the bolt passes through the top and bottom only; the intermediate section being securely held between the top and bottom.
Threaded fasteners have several disadvantages when assembling modules for housing circuit card assemblies. For instance, threaded fasteners increase the time required for assembly and disassembly of a modular enclosure; torque must be applied to each fastener for assembly, which requires additional verification to ensure the proper amount of torque has been applied. Thus, enclosure envelope size is often made larger than necessary for certain uses, in order to accommodate a sufficient number of appropriately sized fasteners to provide adequate clamping pressure. The increased clamping pressure is required to create a seal preventing the contamination of the enclosure from environmental conditions.
In addition to inspecting proper assembly torque application, each fastener must be inspected to make sure it is not missing, that they have been properly installed, and that any additional elements, e.g., lock washer, are also included.
The enclosures are designed to house one or more circuit card assemblies within. Normally, internal circuit card assemblies are fastened to the bottom 16 from the inside and/or are stacked one on top of each other. The circuit card assemblies are positioned and secured inside the enclosure with a required standoff distance from each other. The required distance is achieved by securing mounting bosses or similar hardware onto the mounting panel of the enclosure. When an enclosure contains fewer circuit card assemblies than it is designed to hold, a portion of the enclosure is wasted, and therefore decreases the packing efficiency of the enclosure. One shortfall is that space must be reserved to accommodate fasteners, (e.g., screw heads, washers) on both the upper and lower surfaces of the circuit card assemblies. Should a circuit card assembly be re-laid (i.e., turned), the pre-existing mounting boss locations may become an impediment to circuit routing and component placement. This design requirement is a significant limitation of the existing enclosure designs.
Yet another drawback of the prior art enclosures is the inability to provide adequate electromagnetic interference (EMI) shielding. EMI shielding is pre-planned to maximize efficiency and effectiveness of the enclosure. The efficiency and effectiveness of the pre-planned EMI shielding is reduced when less than the intended number of circuit card assemblies is housed within an enclosure.
Similarly, thermal transfer of heat and electrical grounding are achieved through contact with bosses and/or mounting screws and conveyed through the chassis. Those designs create hot spots and require heat sinks in the vicinity of the bosses to avoid damaging the circuit card assemblies.
In this respect, each enclosure is unique, allowing for very limited expansion of the enclosure to accommodate additional or different circuit card assemblies. Most modular enclosures of the prior art are specifically constructed to house a specific number of circuit card assemblies. This configuration restricts the flexibility of the enclosure to accommodate a varying number of circuit card assemblies.
Furthermore, a necessary characteristic of enclosures for circuit card assemblies is the ability to provide thermal conduction away from the circuit card assemblies. The prior art enclosures utilize mounting bosses to provide the necessary thermal conduction of heat generated on the circuit card assemblies, but the mounting bosses actually in turn transfer that heat to the enclosure structure itself.